雪莲花的染色体进化之路

正染色体是遗传物质的载体,对于物种遗传与进化具有十分重要的作用,其数目和结构变化会导致物种形态、生理、生化、适应等变化。通常物种的染色体数目都是比较保守稳定的,但是一些特殊情况会使植物在形成配子的过程中发生变异,从而导致新形成的合子具有不同的染色体数目变异。自然状态下的物种发生染色体变异受到多种原因的影响,自然环境中紫外辐射、温度变化、机体损伤及其他化学物质刺     

植物单倍体

在植物界细胞染色体的数目因种而异。在植物进化过程中,出现多倍化使染色体数增加;也存在一种相反的情况,即染色体倍性逐渐降低,使染色体数目减少。如在被子植物内系统发育较进化的草本植物的染色体基数比较衰老的的木本植物低;种子植物与蕨类相比,前者又少得多。减少多倍性的一个重要途径是成倍地减少细胞中的染色体数目或单倍化。研究单倍性和单倍体在理论上对于种的细胞遗传结构和进化途径的分析,对数量性状遗传学有重要意义。     

普通小麦与野生二粒小麦A、B基因组的遗传进化关系的SSR分析

以29份普通小麦、野生二粒小麦及野生二粒小麦与节节麦杂交的双二倍体为材料,选取A、B染色体组特异的SSR引物,通过微卫星多态性检测方法探讨上述两物种之间A、B染色体组的遗传进化关系。经NTSYS系统软件UPGMA聚类分析表明,在遗传相似系数为0．18时可以将普通小麦与野生二粒小麦大致分为两大类群,说明野生二粒小麦的A、B染色体组在进化过程中其遗传物质发生了较大变化,但同时野生二粒小麦的D25与D13与普通小麦分为一组,尤其是D13与新疆的红冬麦遗传距离较近,也证明了其两物种间有一定的同源性,并对这些遗传物质分化发生的机制及SSR引物的保守性进行了讨论。     

东北马鹿和东北梅花鹿染色体核型的比较观察及其五种杂交组合后代的组型分析

本文报道了东北马鹿及其与东北梅花鹿的5种杂交组合后代的染色体组型,它们的染色体总臂数NF均为70,X是核型中最大的T,Y则是最小的SM。东北马鹿比东北梅花鹿的染色体多2对T而少1对M。二者的C带、G带带纹、Ag-NOR_s的数目和分布均无明显差异。二者的F_1代之所以能育,作者认为,从东北梅花鹿进化到东北马鹿其染色体进化的主要机制是罗伯逊断裂,遗传物质无明显的增减所致,据此,对动物的分类提出了我们的看法。     

基于短序列测序数据的四倍体拟南芥转录组研究

为了促进对四倍体拟南芥(A.suecica)的研究,阐明多倍体植物在染色体加倍过程中遗传物质的变化,从而在分子层面上解释多倍体植物的环境适应和进化机制,描述了一套基于第二代测序技术的转录组短序列组装和生物信息学分析方法.通过对23 000 000条来至于Illumina测序平台的序列数据进行SOAPdenovo组装,以...     

鹿属(Cervus)染色体组型的进化

鹿属共9个种,除去已绝灭的熊氏鹿(Cervus shomburgki)外,现存者8个种。作者对其中的6个种的染色体组型用外周血培养方法进行了研究。加上文献中已报道的材料,对鹿属中染色体组型已进行分析的共有7个种、13个亚种。对这些材料所进行的分析表明,鹿属动物在进化过程中,X染色体是很保守的,而常染色体的变化,无论是种间还是种内,全是2n数每增加1条,中部或亚中部着丝点染色体数就减少1条,而端着丝点染色体数就增加2条,反之亦然。结合对鹿属古生物学资料和现代各个种的地理分布的分析,作者认为,鹿属染色体进化的主要机制是罗伯逊断裂,即一条中部(亚中部)着丝点染色体在着丝点部位断裂成为两条端着丝点染色体。     

何首乌种质资源核型分析及进化趋势研究

以32份何首乌种质为研究材料,采用常规压片法,对其进行核型分析及进化趋势研究。结果表明:(1)32份何首乌种质存在二倍体(2n=2x=22)和三倍体(2n=3x=33)两种倍型;核型不对称系数As.K%和AI值分别在51.85%～61.52%和0.37～1.40;核型有"1A"、"1B"和"2A"3种类型,属于进化程度较低的植物。(2)在32份何首乌种质中,53.13%的种质为三倍体,表明多倍化在何首乌种质的进化中起着重要作用,但染色体结构变异也是其进化的主要途径之一。(3)何首乌各种质染色体形态变化较大,进化程度参差不齐,可能与种质的生境有一定相关性。(4)何首乌最初的起源中心可能在高纬度地区,在向低纬度地区迁移过程中发生了染色体数目及结构的变化。     

植物细胞核型的进化

生命从诞生开始,在经历了复杂的进化历程之后,才形成了现在丰富多彩的生物世界。在这一进化过程中,作为遗传物质的载体──染色体也发生了相应的进化。并且,核型的进化反映了生物的进化过程及各物种的亲缘关系。因此,对植物的核型进行分析将有助于对植物系统进化的认识。 在生物的进化过程中,物种形成是非常关键的一步。现代达尔文主义认为：生物进化的方式有两种,一是渐进式物种形成,即原来的种经过突变与选择,逐渐积累变异,首先形成地理族和生态族,然后分化成独立的新种。而还有少数学者认为种间进化不同于种内进化,新种形成…     

中国地鼠减数分裂染色体的研究

减数分裂是发生在二倍体生殖细胞形成配子时的一种特殊的细胞分裂。在这一过程中,染色体经历着一系列的复杂变化,即配子的染色体数减半和同源染色体间的遗传物质交换等。因此这方面的研究,无论在细胞遗传的理论或应用上(评价各种诱变因子对性细胞的影响)都具有重要的意义。     

蕨类植物染色体数目研究的好材料

染色体数目分析是现代系统与进化植物学研究十分重要和不可缺少的环节。在蕨类植物中,使用根尖或孢子母细胞作为实验材料的经典方法在取样时往往存在困难。该文以3种桫椤科桫椤属植物为例,探寻适合蕨类植物染色体数目研究的材料。由于取样时没有时间、季节和数量上的限制,我们推荐配子体作为蕨类植物染色体数目研究的实验材料。     

Chromosomal evolution in Cervidae

On the basis of chromosome data obtained on 30 species and 20 subspecies of Cervidae, a report is submitted on the karyosystematics of this family. The primitive karyotype of Cervidae may be inferred to be composed of 35 acrocentric pairs (2n = 70 FN = 70). During the phyletic evolution of this family different types of chromosome rearrangements were probably selected and the group may have differentiated karyologically into three branches: (1) the Cervinae that fixed a centric fusion resulting in a metacentric pair of autosomes (2n = 68, FN = 70), as shown by the basic karyotype of Cervus elaphus, and where Robertsonian fusions are the preeminent type of chromosome rearrangement; (2) the Odocoileinae, in which pericentric inversions and Robertsonian fusions were favored, yielding first a submetacentric X and then a submetacentric autosome pair. The most representative karyotype is 2n = 70, FN = 74--as in Odocoileus hemionus; and (3) the Muntiacinae, in which centric and tandem fusions were the most common chromosome rearrangements. While Muntiacus reevesi has a karyotype 2n = 46, FN = 46, the chromosome number drops down to 2n = 6 in the females of the M. muntjak vaginalis subspecies group and M. rooseveltorum. Therefore, while the karyotypes are conserved within the subfamilies Cervinae and Odocoileinae; the subfamily Muntiacinae appears to be the most chromosomally diversified group. The few karyological data on the Moschus berezovskii suggest that the Moschinae should be placed in a separate family, the Moschidae.     

Phylogenetic relationships among deer in China derived from mitochondrial DNA cytochromeb sequences

The phylogenetic relationships of Cervidae and Moschidae were examined using partial sequence data of mitochondrial DNA (mtDNA) cytochromeb. Ten new sequences were obtained for six species of Cervidae and Moschidae, and aligned with those previously reported for other deer species. Our results demonstrated that the phylogenetic status of the taxa inferred from molecular data was congruent with taxonomy based on morphological studies. Cervidae formed a monophyletic group that consists of four subfamilies: Cervinae, Muntiacinae, Hydropotinae, and Odocoileinae. Moschidae occurred at the base of the Cervidae clade. On the basis of molecular clocks for genetic distance, the divergence time of mtDNA haplotypes within the subfamily Cervinae, among subfamilies in Cervidae, and between Moschidae and Cervidae was estimated to date 2–7 MYA, 6–10 MYA and 8–13 MYA, respectively.     

Cytogenetic aspects of phylogeny in the Bovidae. I. G-banding

An extensive G-banding study of karyotypes of 12 species of Bovidae has been undertaken in an attempt to trace homologies and patterns of evolution of karyotype phenotypes throughout the family. G-banding profiles revealed a considerable degree of chromosome-arm homology throughout the group, which also extended into the related superfamilies, the Giraffoidea and Cervoidea. The conservation of banding patterns in chromosome arms strongly indicates that Robertsonian translocation type rearrangements have provided the major source of interspecies karyotype differences, with inversions and reciprocal and tandem translocations providing relatively minor contributions. Examples of individuals carrying newly arisen Robertsonian translocations are not infrequent, and in one instance there was evidence that two similar rearrangements had arisen independently in two species. Despite the extensive changes in karyotype organization, subfamilies within the Bovidae were characterized by the presence of common rearrangements, and those involving autosomal pairs 11 and 12 of the ox, as well as the X chromosome, separate the Bovinae from the Caprinae and Hippotraginae.     

New phylogenetic perspectives on the Cervidae (Artiodactyla) are provided by the mitochondrial cytochrome b gene.

The entire mitochondrial cytochrome b (cyt b) gene was compared for 11 species of the artiodactyl family Cervidae, representing all living subfamilies, i.e., the antlered Cervinae (Cervus elaphus, C. nippon, Dama dama), Muntiacinae (Muntiacus reevesi), and Odocoileinae (Odocoileus hemionus, Mazama sp., Capreolus capreolus, C. pygargus, Rangifer tarandus, Alces alces); and the antlerless Hydropotinae (Hydropotes inermis). Phylogenetic analyses using Tragulidae, Antilocapridae, Giraffidae and Bovidae as outgroups provide evidence for three multifurcating principal clades within the monophyletic family Cervidae. First, Cervinae and Muntiacus are joined in a moderately-to-strongly supported clade of Eurasian species. Second, Old World Odocoileinae (Capreolus and Hydropotes) associate with the Holarctic Alces. Third, New World Odocoileinae (Mazama and Odocoileus) cluster with the Holarctic Rangifer. The combination of mitochondrial cyt b and nuclear k-casein sequences increases the robustness of these three clades. The Odocoileini + Rangiferini clade is unambiguously supported by a unique derived cranial feature, the expansion of the vomer which divides the choana. Contrasting with current taxonomy, Hydropotes is not the sister group of all the antlered deers, but it is nested within the Odocoileinae. Therefore, Hydropotes lost the antlers secondarily. Thus, the mitochondrial cyt b phylogeny splits Cervidae according to plesiometacarpal (Cervinae + Muntiacinae) versus telemetacarpal (Odocoileinae + Hydropotinae) conditions, and suggests paraphyly of antlered deer.     

Differences in the location of nucleolus organizer regions in European vespertilionid bats

The karyotypes of European vespertilionid bats are distinguished by only a few, easily detectable differences in their G-banding patterns. Most rearrangements can be identified as Robertsonian translocations. Yet, there are surprising differences in the location of active nucleolus organizer regions (NORs), as revealed by silver staining. The ancestral position of the NOR is considered to be a secondary constriction on chromosome 15, as is the case in the genera Eptesicus, Nyctalus, and Vespertilio and in three of four Pipistrellus species. The remaining genera show multiple NOR sites located on minute short arms close to the centromere. In P. pipistrellus, differences in the location of the NORs correlate with the geographical origin of the animals. Some Myotis species possess NORs on numerous chromosomes and show great interindividual variability. In addition, two sibling species, M. brandtii and M. mystacinus, show completely different NOR locations.     

Chromosome evolution in the Salmonidae (Pisces): an update

The karyotypes of salmonid fishes including taxa in the three subfamilies Coregoninae, Thymallinae and Salmoninae are described. This review is an update of the (Hartley, 1987) review of the chromosomes of salmonid fishes. As described in the previous review, the karyotypes of salmonid fishes fall into two main categories based on chromosome numbers: the type A karyotypes have diploid numbers close to 80 with approximately 100 chromosome arms (2n = 80, NF = 100), and the type B karyotypes have diploid numbers close to 60 with approximately 100 chromosome arms (2n = 60, NF = 100). In this paper we have proposed additional sub categories based on variation in the number of chromosome arms: the A' type with NF = 110-120, the A" type with NF greater than 140, and the B' type with NF less than 80. Two modes of chromosome evolution are found in the salmonids: in the Coregoninae and the Salmoninae the chromosomes have evolved by centric fusions of the Robertsonian type decreasing chromosome numbers (2n) while retaining chromosome arm numbers (NF) close to that found in the hypothetical tetraploid ancestor so that most extant taxa have either type A or type B karyotypes. In the Thymallinae, the chromosomes have evolved by inversions so that chromosome arm numbers (NF) have increased but chromosome numbers (2n) close to the karyotype of the hypothetical tetraploid ancestor have been retained and all taxa have type A' karyotypes. Most of the taxa with type B karyotypes in the Coregoninae and Salmoninae are members of the genus Oncorhynchus, although at least one example of type B karyotypes is found in all of the other genera. These taxa either have an anadromous life history or are found in specialized lacustrine environments. Selection for increases or decreases in genetic recombination as proposed by Qumsiyeh, 1994 could have been involved in the evolution of chromosome number in salmonid fishes.     

Numerical and structural variations of the X chromosomes and no. 2 autosomes in mandarin vole, Microtus mandarinus (Rodentia)

Here we describe our studies on Microtus mandarinus faeceus of Jiangyan in Jiangsu province of China. By karyotype and G-banding analysis we have found variation in chromosome number and polymorphisms of the X chromosome and the second pair of autosomes of the subspecies. Chromosome number of the subspecies is 2n=47-50. The subspecies has three kinds of chromosomal sex: XX, XO and XY, among which one of the X chromosomes is subtelocentric (X(ST)) and the other is metacentric (X(M)). After comparing karyotypes of different subspecies, we found the specific cytogenetic characteristics of Microtus mandarinus, that is they have three kinds of chromosomal sex: XX, XO and XY; X chromosomes are heteromorphic; the chromosome number of female individuals are one less than male individuals; chromosome number of XX individuals are equal to that of XO ones. We hypothesize that Robertsonian translocation is the main reason of the polymorphism of the second pair of autosomes and variety of chromosome number, and it also causes the chromosome number evolution in different subspecies of Microtus mandarinus.     

Mutation rates of structural chromosome rearrangements in man.

The gametic mutation rates of human structural chromosome rearrangements have been estimated from rearrangements ascertained from systematic surveys of live births and spontaneous abortions. The mutation rates for rearrangements that survive long enough to give rise to clinically recognized pregnancies are 2.20 X 10(-4) for balanced rearrangements, 3.54 X 10(-4) for unbalanced Robertsonian translocations, and 3.42 X 10(-4) for unbalanced non-Robertsonian rearrangements. These estimates give a mutation rate for all detectable structural chromosome rearrangements of approximately 1 X 10(-3). The most common single rearrangement, the Robertsonian translocation involving chromosomes 13 and 14, has a mutation rate of 1.5 X 10(-4).     

Phylogeny and evolution of Cervidae based on complete mitochondrial genomes

Mitochondrial DNA sequences can be used to estimate phylogenetic relationships among animal taxa and for molecular phylogenetic evolution analysis. With the development of sequencing technology, more and more mitochondrial sequences have been made available in public databases, including whole mitochondrial DNA sequences. These data have been used for phylogenetic analysis of animal species, and for studies of evolutionary processes. We made phylogenetic analyses of 19 species of Cervidae, with Bos taurus as the outgroup. We used neighbor joining, maximum likelihood, maximum parsimony, and Bayesian inference methods on whole mitochondrial genome sequences. The consensus phylogenetic trees supported monophyly of the family Cervidae; it was divided into two subfamilies, Plesiometacarpalia and Telemetacarpalia, and four tribes, Cervinae, Muntiacinae, Hydropotinae, and Odocoileinae. The divergence times in these families were estimated by phylogenetic analysis using the Bayesian method with a relaxed molecular clock method; the results were consistent with those of previous studies. We concluded that the evolutionary structure of the family Cervidae can be reconstructed by phylogenetic analysis based on whole mitochondrial genomes; this method could be used broadly in phylogenetic evolutionary analysis of animal taxa.     

The pattern of phylogenomic evolution of the Canidae

Canidae species fall into two categories with respect to their chromosome composition: those with high numbered largely acrocentric karyotypes and others with a low numbered principally metacentric karyotype. Those species with low numbered metacentric karyotypes are derived from multiple independent fusions of chromosome segments found as acrocentric chromosomes in the high numbered species. Extensive chromosome homology is apparent among acrocentric chromosome arms within Canidae species; however, little chromosome arm homology exists between Canidae species and those from other Carnivore families. Here we use Zoo-FISH (fluorescent in situ hybridization, also called chromosomal painting) probes from flow-sorted chromosomes of the Japanese raccoon dog (Nyctereutes procyonoides) to examine two phylogenetically divergent canids, the arctic fox (Alopex lagopus) and the crab-eating fox (Cerdocyon thous). The results affirm intra-canid chromosome homologies, also implicated by G-banding. In addition, painting probes from domestic cat (Felis catus), representative of the ancestral carnivore karyotype (ACK), and giant panda (Ailuropoda melanoleuca) were used to define primitive homologous segments apparent between canids and other carnivore families. Canid chromosomes seem unique among carnivores in that many canid chromosome arms are mosaics of two to four homology segments of the ACK chromosome arms. The mosaic pattern apparently preceded the divergence of modern canid species since conserved homology segments among different canid species are common, even though those segments are rearranged relative to the ancestral carnivore genome arrangement. The results indicate an ancestral episode of extensive centric fission leading to an ancestral canid genome organization that was subsequently reorganized by multiple chromosome fusion events in some but not all Canidae lineages.